1. Field of the Invention
The present invention relates to insulated steel doors, and in particular, doors having an internal structure for improving rigidity, thermal efficiency, aesthetics and manufacturability.
2. Description of Related Art
Insulated exterior steel doors include an insulation material to resist heat transfer from one side of the door to the opposing side. Typically, the door contains a foam panel for insulation, for example, as described in ANSI/NAAMM HMMA 867-06 part 2.01.A.2.a-d. The insulation provides for a thermally efficient door, but the insulation in an otherwise hollow door provides very little structural integrity.
Steel doors which include structural stiffening elements are usually thermally inefficient due to the transfer of heat from the door interior to the door exterior through the structural elements, for example, as described in ANSI/NAAMM HMMA 867-06 part 2.01.A.2.e. Additionally, where the structural elements are welded to the door skin, weld marks are usually apparent.